Heart failure is an increasing health problem worldwide. Five million people in the United States and 15 million people among the 900 million people represented by the European Society of Cardiology (ESC) are suffering from heart failure. A similar number of people have asymptomatic cardiac dysfunction.
Heart failure conditions may be characterized by weakness, breathlessness, abdominal discomfort, edema in the lungs and the lower portions of the body. These symptoms are associated with the inability of the heart to pump sufficient amounts of blood without unduly raising filling pressures. Insufficiency may be associated with either the left ventricle, the right ventricle, or both. Heart failure may be caused by inefficient contractions caused by a disturbed physiologic conduction system. This disturbance may be caused by, for instance, ischemia, infarction, fibrosis or dilatation.
A possible approach of treating patients suffering from various heart failure conditions is to use an implantable medical device, such as a pacemaker, providing cardiac pacing to the failing heart. For instance, cardiac pacing to resynchronize ventricular contractions has been shown to increase cardiac output and has been observed to produce reverse cardiac remodelling in human clinical studies.
Cardiac pacing can be achieved by applying a pacing pulse to a selected portion of the heart, in particular to the ventricles of the heart. In the art, such a pacing pulse has been applied at or close to the apex of the ventricles to cause propagation of a depolarization wave towards the base of the ventricles to start the contraction of the ventricles close to the heart apex and then move the contractile pattern towards the semilunar valves. It is believed that such a pacing and resulting contractive pattern will efficiently empty the blood present in the ventricles through the aortic valve and the pulmonary valve and into the aorta and the pulmonary artery, respectively.
The traditional apex-to-base stimulation approach is, though, different from the true cardiac motion occurring following intrinsic depolarization during a cardiac cycle. In particular, apex-to-base stimulation may have an increased risk of mitral regurgitation during systolic emptying of the ventricles.
US 2004/0106958 discloses an implantable medical device connected to a multi-electrode lead positioned in the right ventricle and designed to treat congestive heart failure. An electrode mapping procedure is conducted in order to identify optimal stimulating electrode of the multiple electrodes on the lead. The mapping procedure can be conducted in order to find a suitable stimulating electrode near the right ventricular outflow tract to reduce mitral regurgitation.
The U.S. patent application can thereby be used to reduce the risk of mitral regurgitation but still has limitations in terms of not achieving optimal cardiac movement during systolic pacing of the heart.
Circulation Cardiovascular Imaging 2009, 2: 444-450 discloses that mitral regurgitation in heart failure patients can be reduced with cardiac resynchronization therapy (CRT). It was concluded that reduction in functional mitral regurgitation after CRT is associated with improved left ventricular closing pressures on the mitral valve. CRT results in more sustained peak closing pressures on the mitral valve during systole as demonstrated by a higher closing pressure ratio after CRT due to improved left ventricular contractility and/or improved coordination of left ventricular contraction.
Although reducing the problems associated with mitral regurgitation, the proposed CRT therapy does still not achieve optimal cardiac movement during systolic pacing of the heart.